Sulfuric acid extraction of isobutylene from hydrocarbon mixtures



Patented July 15, 1947 SULFURIC ACID EXTRACTION OF ISOBU- TYLENE FROM HYDROCARBON MIXTURES John W. Packie, Green Village, and Walter H. Rupp, Mountainside, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application September 12, 1944, Serial No. 553,704

6 Claims.

The present invention relates to the separation of olefins from mixtures of olefins and saturated hydrocarbons which are associated in g seous and liquid hydrocarbon mixtures, and more particularly it relates to the separation of isobutylene from mixtures of hydrocarbons consisting mainly of olefins and saturated hydrocarbons having 4 carbon atoms to the molecule.

There are many chemical processes in which it is a decided advantage to use a substantially pure olefin, unmixed with inert diluents, such as saturated hydrocarbons. For example, in chemical reactions with the gaseous olefins in which pressure is advantageous, the effective pressure is normally the partial pressure of the reactive olefin in the mixture. In such cases, substantially pure olefins permit much lower pressures to be employed and less gas to be compressed than in the case of a gas mixture poor in reactive olefin. Also in many cases the olefin reaction may be reversible, the proportion of the desired product being dependent upon the concentration of reactive olefin in the mixture. In such cases, the dilution of the olefin with an inert diluent, such as a saturated hydrocarbon, may so aifect the yield of the desired reaction product as to render the process unprofitable. Also the desired reaction product may be very volatile, as for example, ethyl chloride and the like, or the chemical reagent used to react with olefin may be very volatile and carried away by the inert diluent.

It is also desirable to have isobutylene free of normal butylenes when the isobutylene is to be polymerized or copolymerized to high molecular weight resins.

The separation of isobutylene by fractional distillation from the saturated hydrocarbons, other olefins and diolefins having the same number of carbon atoms to the molecule is very difficult, due to the closeness of the boiling points of the various hydrocarbons having 4 carbon atoms to the molecule, which are as follows:

Boiling point C. Isobutane 12.2 Isobutylene -6.8 l-butylene -5.0 Butadiene -2.6 n-Butane -0.3 2-butylene, trans +0.96 Z-butylene, cis +3.73

It has been previously proposed to separate the simple olefins from saturated hydrocarbons by reacting the olefins with various metallic salts with which the olefins form labile combinations and from which the olefin may be regenerated. Certain salts of silver, mercury and copper have been suggested for this purpose, but in commer- 2 cial practice the use of such salts was found in most. cases to be economically unfeasible.

It is also known that isobutylene may be readily absorbed by contacting it in admixture with other hydrocarbons with sulfuric acid of 55-75% concentration. At the present time this is accomplished in one of two ways. One process involves the use of about a 60 to by weight concentrations sulfuric acid at a temperature of about 60 F., the acid being saturated to the extent of 0.5 mol of olefin per mol of sulfuric acid. The other process is similar but the extraction temperature is maintained at about 100 F. and

the saturation at about 1.5 mols of olefin per mol of sulfuric acid. Although y the use of the first process a smaller amount of normal butylenes is absorbed along with the isobutylene and a smaller amount of isobutylene is polymerized in the extraction zone, this process has the disadvantage that it requires a large amount of refrigeration and uses a larger quantity of acid than is required when operating at the higher temperature of the second mentioned process.

It is therefore, the object of the present invention to absorb isobutylene in sulfuric acid under such conditions that a very small amount of normal butylenes is absorbed along with the isobutylene While simultaneously avoiding the use of large amounts of acid and reducing the amount of refrigeration required.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing which represent one method by which this invention may be carried out.

According to the present invention, these objects are attained by absorbing a C4 fraction, containing paraffins, secondary and tertiary olefins in sulfuric acid in two stages using a higher temperature in the first stage than in the second, a partially spent acid being used as the absorbent in the high temperature stage and fresh acid in the low temperature stage. In the preferred form of the invention the C4 hydrocarbon fraction, either in the gaseous or liquid state, is contacted with the partially spent acid from the low temperature stage at a temperature between and 110 F., preferably F. in any suitable manner. For example, resort may be had to agitation in a common vessel or to countercurrent flow. It is desirable when employing the C4 fraction in a gaseous state to conduct the process in countercurrent fashion through a packed tower as this system lends itself most readily to intimate distribution of the tertiary base olefin in the absorbent. By using an acid extract as the absorbent which contains from 0.2 to 0.6 mol of isobutylene per mol of 100% sulfuric acid and operating at a temperature between 90 and F.

3. 65 to 85% of the isobutylene in the Cifraction is absorbed without any substantial absorption of the secondary olefins. The unabsorbed 15 to 35% isobutylene is then absorbed in fresh sulfuric acid having a concentration between 60 and 65%, preferably 65%, at a temperature between 55 and 75 F., preferably 60 F. The contact between the acid and the olefin may be carried out in any manner as described above but is likewise preferably carried out in a packed column. The acid extract thus formed contains between 0.2 and 0.6 mol of isobutylene per mol of 100% sulfuric acid and is particularly suitable for use as the absorbent in the high temperature stage.-

Referring now to the drawing, a C4 fraction is introduced through line I and mixed with partially spent sulfuric acid containing alkyl sulfates circulating in line 2. The mixture is then passed through cooler 3 and introduced into absorber 4 through lines 5 and 6, where the mixture of C4 fraction and partially spent acid is' contacted in any suitable manner. For example, resort may be had to the agitation of the two agents in a common vessel or to countercurrent flow. It is to be understood, however, that the dispersion in absorber 4 can be obtained in any other desired manner such as by turbo-mixers, baflles, orifices, perforated plates, etc. A particularly desirable methodfor obtaining good contact in absorber 4 is by introducing the mixture through jets 1. Absorber 4 is maintained at a temperature between 90 and 110 F., preferably at 100 F. In this absorber the majority of the isobutylene (65-85% of the total isobutylene extracted) is removed. Un'absorbed hydrocarbons plus some acid extract if desired are removed from absorber 4 through line 8 and passed through line 9 into settler ID. If desired a portion of the unabsorbed hydrocarbons plus extract may be passed through II and introduced into line 2 and thus recycled to absorber 4. A portion of the sulfuric acid solution containingthe absorbed isobutylene in the form of an emulsion with some of the hydrocarbon is removed from absorber 4 through line I2 and passed through line l3 to settler I 0. A portion of the emulsion is passed to line 2 for recycling through cooler 3 to the absorber for removal of heat and for agitation in the absorber.

From settler Hi the acid extract containing from 1.0 to 1.8 mols of isobutylene per mol of 100% sulfuric acid is removed through line l4 and disposed of as desired. For example, it may be'processed to regenerate the isobutylene absorbed therein, or it may be processed to polymerize its contained isobutylene. Unabsorbed hydrocarbons are removed from settler 10 through line l6 to line I3 into which fresh sulfuric acid of 60-65% concentration is introduced through line 18. The mixture of unabsorbed hydrocarbon and fresh sulfuric acid plus some recycle emulsion is then pumped through line 19 to cooler 20. Refrigeratedby a cooling medium such as ammonia or brine, from cooler 20 the mixture is passed through line 2| and branch lines 22 and 23 into absorber 24, which is constructed preferabl along the same lines as absorber 4.

As described in connection with absorber 4 intimate contact between the unabsorbed hydrocarbon and the fresh sulfuric acid may be obtained in any suitable manner but is preferably obtained by the use of jets 25. Absorber 24 is maintained at a temperature lower than that obtaining in absorber 4, for example 55-75" F., preferably 60 F. In this manner the remaining 4 15-35% of isobutylene contained in the hydrocarbons is removed.

Unabsorbed hydrocarbons such as paraflins, butene-l and butene-2 are removed from absorber 24 through line 26 and passed through line 21 into settler 28. As in case of absorber 4 a portion of these unabsorbed hydrocarbons may be passed through line 29 into line l9 andthus recycled to absorber 24. The emulsion is removed from the bottom of absorber 24 through line 30 and passed through line 3| into settler 28. A portion of the emulsion may likewise be passed through line 32 and introduced through recycle line I9 and returned to the absorber 24.

In settler 28 the effluent stream settles into two phases, an upper hydrocarbon phase and a lower extract phase. The lower extract phase containing from 0.2 to 0.6 mol of isobutylene/mol of sulfuric acid is withdrawn through line 33 and introduced into line 2 for use as the absorbing medium in absorber 4. The upper hydrocarbon phase comprising unabsorbed hydrocarbons is removed from settler 28 through line 35 and passed to storage.

By means of the above described process only a very small amount of normal butylene is absorbed in the acid extract along with the isobutylene and also only a very small amount of isobutylene is polymerized in the absorption zone. Furthermore, the majority of the heat of reaction is removed by water cooling in the first stage and refrigeration islimited to the second stage.

By way of illustration the following typical yields and operating conditions are obtainable in this process:

1. Hydrocarbon feed Per cent by weight Isobutylene 35 1 Representing 97% of isobutylene in feed. Representing 2% of the normal butylene in the feed.

4. Operating conditions A. High temperature stage at 100 F.

Extract saturation, 1.5 mols isobutylene/mol Pressure on absorber, 100 lbs. gauge.

Extract/hydrocarbon ra t i o in emulsion,

Low temperature stage at 60 F.

Extract saturation, 0.5 mol isobutylene/mol Pressure on absorber, 100 lbs. gauge.

Extract/hydrocarbon r a ti o in emulsion,

C. Hydrocarbon residence time in each stage,

30 minutes. 1). Acid strength, 65% H2304 by weight.

From the above data. it is apparent that the present invention effectively increases the-olefin purity since very little secondary olefins are absorbed in the acid along with the isobutylene, 97% of the isobutylene and only 2% of the normal butylenes being absorbed in the extract from the high temperature stage.

Although the present invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction of the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

The nature and objects of the present invention having thus been set forth and specific illustration of the same given, what is claimed as new and useful and desired to be secured by Letters Patent is:

1. A continuous process for the selective removal of isobutylene from hydrocarbon mixtures containing parafiins, secondary and tertiary olefins, comprising contacting the hydrocarbon mixture in a first stage at a temperature between 90 and 110 F. with sulfuric acid containing dissolved isobutylene to selectively dissolve the major portion of the isobutylene contained in said hydrocarbon mixture, separating the solution of the isobutylene in sulfuric acid from the undissolved hydrocarbon mixture, contacting the undissolved hydrocarbon mixture in a second stage at a temperature between 55 and 75 F. with fresh sulfuric acid having a strength between 60 and 70% by weight to selectively dissolve the re-- mainlng portion of the isobutylene from. said hy-' drocarbon mixture, and recycling the solution of isobutylene in sulfuric acid from the second stage to said first stage for use therein as the medium for dissolving further amounts of isobutylene.

2. A continuous process for the selective removal of isobutylene from hydrocarbon mixtures containing parafilns, secondary and tertiary olefins, comprising contacting the hydrocarbon mix. ture in a, first stage at a temperature of about 100 F. with sulfuric acid containing dissolved isobutylene therein, separating the solution of isobutylene in sulfuric acid from the undissolved hydrocarbon mixture, contacting the undissolved hydrocarbon mixture in a second stage at a temperature of about 60 F. with sulfuric acid of a concentration of 65% by weight, and recycling the solution of isobutylene in sulfuric acid from the second stage to the first stage for use in dissolving further amounts of isobutylene therein.

3. A continuous process for the selective ree moval of isobutylene from hydrocarbon mixtures containing parafiins, secondary and tertiary olefins, comprising contacting the hydrocarbon mixture in a first stage at a temperature between 90 and 110 F, with sulfuric acid containing from 0.2 to 0.6 mol of isobutylene per mol of 100% suifuric acid to yield an acid extract containing 1.0 to 1.8 mols of isobutylene per mol of 100% sulfuric acid, separating the acid extract containing the dissolved isobutylene from the undissolved hydrocarbon mixture, contacting the undissolved hydrocarbon mixture in a second stage at a temperature between 55 and 75 F. with fresh sulfuric acid having a strength between and by weight to selectively dissolve the remaining portion of the isobutylene from said hydrocarbon mixture.

4. A continuous process for the selective removal of isobutylene from hydrocarbon mixtures containing parafllns, secondary and tertiary olefins, comprising contacting the hydrocarbon mixture in a first stage at a temperature about F. with sulfuric acid containing 0.5 mol of isobutylene per mol of 100% sulfuric-acid to yield an acid extract containing 1.5 mols of isobutylene per mol of 100% sulfuric acid, separating the solution of isobutylene in sulfuric acid from the undissolved hydrocarbon mixture and contacting the undissolved hydrocarbon mixture in a second stage at a temperature about 60 F. with sulfuric acid of a concentration of 65% by weight.

5. Process according to claim 3 in which the solution of isobutylene in sulfuric acid from said second stage is recycled to said first stage as the medium for dissolving isobutylene therein.

6. Process according to claim 4 in which the solution of isobutylene in sulfuric acid from said second stage is recycled to said first stage as the medium for dissolving isobutylene therein.

JOHN W, PACKIE. WALTER H. RUPP.

REFERENCES CITED The following references are of record in the file of this patent: 1

UNITED STATES PATENTS Number Name Date 1,953,618 Kramer Apr. 3, 1934 1,998,411 Merley Apr. 16, 1935 2,190,501 Brooks Feb. 13, 1940 2,350,558 Kerns et al June 6, 1944 2,128,971 Snow Sept. 6, 1938 1,991,948 Lacy Feb. 19, 1935 2,345,114 Guinot Mar. 28, 1944 2,300,818 Sweeney et a1 Nov. 3, 1942 2,173,452 Merley Sept. 19, 1939 2,355,480 Morrell Aug. 8, 1944 

